I agree, the notebook-lineup is a bit confusing at the moment. It would have made perfect sense to introduce the rMB as the new MacBook Air, while the MacBook Air could have been rebranded as a "MacBook". Thus, leaving:
* MacBook - Classic, entry-level notebook (the MBA). Does a lot of things very well, but isn't best at anything. A great compromise between power and portability, for the average user, lacks in areas such as screen-quality.
* MacBook Air - The super slim, ultra portable computer. Decent performance, but oh so thin. Form over function, for those who are willing to sacrifice some speed and ports for thinness and light weight.
* MacBook Pro - For the Pro in you. Power and speed above all else.
As of now, it makes no sense having an "Air" which is thicker and heavier than the normal "MacBook".